The present invention relates to a temperature detector, and more particularly to a temperature detector comprising semiconductor having good linearity of the change of resistivity of the semiconductor to the change of temperature at a low temperature of not more than 100 K.
In general, there have been employed as a contact-type temperature detector a thermocouple, resistance thermometer bulb utilizing a metal such as platinum or thermistor utilizing semiconductor, or the like.
Hitherto, at a low temperature of not more than 100 K., there has been employed a temperature detector using carbon solid resistor which is often employed in an electronic circuit. This kind of sensor measures the temperature by utilizing a phenomenon that the resistivity of the carbon solid resistor changes with the change of temperature. The carbon solid resistor is obtained by adding powder of insulation such as clay, silica and talc to graphite, adding further binding material such as phenol resin and then hot forming the obtained mixture.
The above-mentioned carbon solid resistor has, however, problems in that the temperature dependency of the resistivity of graphite is complex and the reproducibility of resistivity is poor, because the resistor shows metallic property or semiconductive property in compliance with the direction of crystallographic axis due to very large anisotropic of graphite.
Further, there has been hitherto employed a thermistor using germanium as a temperature detector. The thermistor comprises a single crystal of germanium whereinto an impurity such as phosphorus is mixed. In this thermistor, the temperature is measured by detecting the change of resistivity with the change of temperature.
This kind of thermister is superior to the above-mentioned carbon solid resistor in reproducibility of resistivity. It, however, has problems that it is apt to be influenced by a magnetic field, it cannot represent a temperature dependency in one formula over a wide range of temperature, and it costs too much.
The present invention was made in order to solve the above drawbacks and to provide a temperature detector having good linearity of temperature dependency of resistivity even at a low temperature of not more than 100 K.